Welding, Cutting & Allied Processes and Arc Welding Power Sources (Welding Machines)

Fundamentals of Threaded Fasteners

Information about mechanical properties and identification markings for threaded fasteners as per the International Organization for Standardization (ISO) specifications for the metric fasteners and as per American Society for Testing and Materials (ASTM) and SAE International (Society of Automotive Engineers) specifications for the imperial fasteners is given in the following booklet. Information about mechanical properties and selection of fastener material is also given in the booklet.

Mechanical Properties and Identification Markings for Threaded Fasteners

Most industrial threaded fasteners are covered by two basic standards: one for materials and properties called materials standards; the other, for dimensions and tolerances called product standards. Information about product standards for industrial threaded fasteners is given in the following booklet.

Product (Dimensions and Tolerances) Standards for Threaded Fasteners

A bolted joint is designed considering that when the bolts are preloaded as designed, the joint will fulfil its designed function. Hence, equally important to use of the designed bolts in a bolted joint in determining joint performance is the assembly procedure. In view of this, information about installation/tightening of threaded fasteners (nuts and bolts) and locking methods for threaded fasteners is given in the following booklet. During maintenance of threaded fasteners, sometimes it is required to use helical coil inserts and tap threads. Hence, information about helical coil inserts, tapping of screw thread and other useful information for maintenance is also given in the booklet.

Installation and Maintenance of Threaded Fasteners (Nuts and Bolts)

Seals are incorporated into a mechanical assembly containing fluids to prevent their leakage at the points where different parts of the assembly meet. An O-ring seal is one of the most widely used seal. It is also known as toroidal seal. An O-ring seal is used in applications, ranging from garden hose couplings to aerospace or oil and gas duties as it is a simple, space saving and cost effective design. In view of this, information about construction, working, properties of elastomeric (rubber) compounds, design considerations, size (dimensions) standards, quality acceptance criteria, installation guidelines, storage, and maintenance (failure analysis) of O-rings is given in the following booklet.

Working, Design Considerations and Maintenance of O-rings

Information about construction, installation, maintenance and troubleshooting for flexible couplings is given in the following article.

Construction, Installation and Maintenance of Flexible Couplings

Keyless shaft locking devices/assemblies/elements/bushings (also called friction locks or shaft to hub connections) are standard machine elements used to connect shafts and hubs. They are capable of transmitting torque, radial forces, axial forces and bending moments. They also have many advantages over traditional methods. In view of this, information about construction, working and installation of keyless shaft locking devices is given in the following article.

Construction, Working and Installation of Keyless Shaft Locking Devices

Fluid couplings or hydraulic couplings work on the hydrodynamic principle. Fluid couplings are often used to drive large inertia machines in combination with squirrel cage motors. They permit a load free acceleration of the motor and consequently with increasing oil fill, provide a soft/gentle quasi steady state start-up of the machine. They are used in drives for conveyor systems and in heavy industry. Information about construction, working, installation, operation and maintenance of a fluid coupling is given in the following article.

Construction, Working, Operation and Maintenance of Fluid Couplings

Freewheels are “overrunning” clutches, i.e., they will drive in one direction but overrun (freewheel) in the other direction. They are used as backstops, overrunning clutches and indexing freewheels. Freewheels are widely used as backstops. A backstop when mounted on an inclined conveyor head shaft is commonly called holdback. Information about construction, working and installation of freewheels is given in the following article.

Construction, Working and Installation of Freewheels (Backstops/Holdbacks)

Electro hydraulic thruster drum brake is a device used to retard the speed of moving machinery and to stop it accurately to the desired position. Thruster operated drum brakes are spring applied and electrically released. These brakes are mainly used in material lifting and handling equipment in the field of applications like ports, steel and metallurgy, mining, etc. mainly because of their “smooth” braking and 'fail-to-safety' designs to ensure safety to men and machines. In view of this, information about construction, working, installation and maintenance of electro hydraulic thruster drum brakes and thrusters is given in the following article.

Construction, Working and Maintenance of Electro Hydraulic Thruster Drum Brakes

V-belt drive systems (also called friction drives) are an economical option for transmitting power in industrial, automotive, commercial, agricultural and home appliance applications. To derive maximum benefit from a well-designed V-belt drive, it is important that the simple installation and maintenance procedures are closely followed. In view of this, information about construction, installation and maintenance of power transmission V-belt drives is given in the following booklet.

Construction, Installation and Maintenance of Power Transmission V-Belt Drives

Pivoted motor bases are widely used to automatically control the belt’s tension to minimize maintenance and maximize belt life. In view of this, information about construction and working of pivoted motor bases, also called reactive torque motor bases for belt drives is given in the following article.

Construction and Working of Pivoted Motor Bases for Belt Drives

Bulk material handling plants have become the backbone of many production/processing plants because production gets severely affected if the bulk material handling plant is not available. As a belt conveyor is a very important equipment of coal handling plants and bulk material handling plants, information about belt conveyors, chutes and systems / accessories (for example, dust suppression system, belt cleaners, etc.) related with conveyors and chutes is given in the following booklet.

Construction and Maintenance of Belt Conveyors for Coal and Bulk Material Handling Plants

To reduce sulfur emissions or non-availability of traditional coal, there has been a shift in recent years from use of more traditional bituminous coal to subbituminous coal, such as Powder River Basin (PRB) coal and Indonesian coal like ENVIROCOAL by PT Adaro, Indonesia. These coals tend to react with oxygen in the air and have tendency for spontaneous combustion. This has resulted in fires at facilities that previously had excellent safety records.

In view of above, important information on spontaneous combustion of coal and care to be taken for their use in a power plant is given in the following article. The information will be useful for coal storage and coal transportation also.

Spontaneous Combustion of Coal

Electric vibrators (electromagnetic vibrators and unbalanced motors) are used during emptying bulk materials from silos / hoppers. In a bulk material processing plant, screening of material is carried out for various applications. Many of these application use vibrating screens. In view of this, information about construction, working and maintenance of electric vibrators and vibrating screens is given in the following booklet.

Construction, Working and Maintenance of Vibrators and Vibrating Screens

Crushers and breakers are used to reduce size of mined and quarried material for further processing or to size suitable for the intended end use. Information about construction, working and maintenance of various type of crushers (Gyratory Crushers, Jaw Crushers, Cone Crushers, Roll Crushers, Low Speed Sizers, Horizontal Shaft Impactors, Ring Granulators and Rotary Breakers) for crushing bulk materials is given in the following booklet.

Construction, Working and Maintenance of Crushers for Crushing Bulk Materials

Most of the time bulk material is received by process plants by railway, ship / barge or truck. As the quantity of the material received is huge, it needs mechanized means for unloading it. In view of this, information about construction, working and maintenance of systems viz. wagon tippling systems (wagon tipplers), track hopper systems, ship unloaders and truck unloaders for unloading bulk materials is given in the following booklet.

Construction, Working and Maintenance of Equipments for Unloading Bulk Materials

Since bulk materials arrival time at a plant is much shorter as compared to their consumption time, they require to be stocked/stored. Due to this, stackers are needed to create stockpiles of the bulk materials. Buffer storage of the bulk materials is also necessary to take care of any disruptions in the transport system or in the mines due to which material cannot be received at the plant on such days. The material so stored needs to be retrieved (reclaimed) to suit its gradual consumption in the plant. Therefore, stock yard needs reclaimer machines to reclaim the material. In view of this, information about construction, working and maintenance of stackers and reclaimers for bulk materials is given in the following booklet.

Construction, Working and Maintenance of Stackers and Reclaimers for Bulk Materials

Construction, Working, Operation and Maintenance of Liquid Ring Vacuum Pumps

Information on Elastomers

Information about plastics is given in the following article.

Information on Plastics

Information about fundamentals of gearboxes (gear drives) is given in the following booklet.

Fundamentals, Selection, Installation and Maintenance of Gearboxes (Gear Drives) – Part 1

Information about selection, installation and maintenance of gearboxes (gear drives) is given in the following booklet.

Fundamentals, Selection, Installation and Maintenance of Gearboxes (Gear Drives) – Part 2

Maintenance of Ash Handling Plants and Pneumatic Conveying Systems

Selected information about ash handling plants from standard design criteria / guidelines for balance of plant of 2 x (500 MW or above) thermal power project published by Central Electricity Authority, New Delhi, India – 110066, in September 2010 is given in the following article.

CEA Guidelines for Ash Handling Plants

Information about construction, working, operation and maintenance of electrostatic precipitators (ESPs) is given in the following booklet.

Construction, Working, Operation and Maintenance of Electrostatic Precipitators (ESPs)

Information about working, design considerations and maintenance of bag type fabric filters (mechanical shaker, reverse air and pulse jet type) is given in the following booklet.

Working, Design Considerations and Maintenance of Bag Type Fabric Filters

Information about construction, working, operation and maintenance of liquid ring vacuum pumps is uploaded in the Pumps category of this website.

• NDT Resource Center: Resources at Education at Material Premier – http://www.ndt-ed.org
• Multimedia Group, Department of Engineering, Cambridge University, UK: Teach Yourself Phase Diagrams – http://www-g.eng.cam.ac.uk/mmg/teaching
• Steel Matter: http://www.matter.org.uk/steelmatter
• University of Bolton, UK: Basic principles of materials – http://www.ami.ac.uk/courses/topics
• Key to Metals: Resource Center at Articles – http://www.keytometals.com
• SubsTech (Substances & Technologies): http://www.substech.com
• AISI (American Iron and Steel Institute): Learning Center – http://www.steel.org
• Corus: Internet Teaching Resources – http://www.corusgroup.com/en/responsibility/education/resources/internet
• Tata Steel International (Australasia) Ltd: Products – http://tatasteelnz.com
• BRITISH STAINLESS STEEL ASSOCIATION: Technical Help – http://www.bssa.org.uk
• The Nickel Institute: Nickel & Its Uses at Technical Support – http://nickelinstitute.org
• The International Stainless Steel Forum (ISSF): http://www.worldstainless.org
• EverBright(China) St. St. Pipe Co., Ltd: Reference – http://www.eb-stainless.com
• Ductile Iron Society: Ductile Iron Data – http://www.ductile.org
• Steel Founders Society of America: Publications – http://sfsa.org

Strength of a Metal/Alloy

The strength of a metal/alloy can be described as the resistance against the onset of plastic deformation under an external load. Plastic deformation occurs by the movement of dislocations through the metal (in this article, generally metal word will be used for metal or an alloy) lattice which enables single lattice planes to slip consecutively over one another. If this motion is hindered by lattice defects, a higher external load must be applied so that the dislocations can overcome the obstacles. It is for this reason that means of increasing the strength of steels always aim at hindering dislocation movement. Various obstacles to dislocation motion are as per the table given below.

Solid Solution Strengthening

Solid solution strengthening occurs when the atoms of the new element (solute) form a solid solution with the original element (solvent), but there is still only one phase.

The increase in strength is produced by solute atoms which are dissolved in the metal matrix (solvent). Since solute atoms differ in size as compared to the atoms of metal matrix they introduce tensile or compressive lattice strains (lattice distortion) that hinders the movement of dislocations. The increase of yield stress depends on the kind, amount and distribution of the solute atoms. Solute atoms, those dissolve interstitially between the atoms of the matrix results in a high lattice distortion (e.g. C and N) as compared to others which dissolve substitutionally and occupy regular lattice positions (e.g. Cr).

Increasing strength by solid solution strengthening leads to a decrease in toughness (Toughness is the ability of a material to avoid brittle fracture. Toughness = Strength + Ductility).

Strain Strengthening

Linear lattice defects are the dislocations themselves. The lattice distortion surrounding the dislocation disturbs the movement of other dislocations. A dislocation in the path of other dislocation can act as an obstacle to the motion of the latter. This interaction increases with increasing dislocation density.

When cold forming steel, e.g. cold rolling, dislocations are continuously produced because they permanently block each other. The dislocation density rises and increases the strength of the steel. Such strengthening is accompanied by a pronounced reduction in toughness.

Grain Refinement

Grain refinement is the most important strengthening mechanism because it is the only method of strengthening which is accompanied by an increase in resistance to brittle fracture. The toughness of the alloy also increases as grain size decreases.

As shown in the figure given below, slip planes do not cross from one grain to another but are confined by the grain boundaries. Due to this, in large grains there is more slippage and greater plastic deformation. In small grains, slip process is confined and results in small slippage.

During plastic deformation, slip or dislocation motion must take place across the common grain boundary, which acts as a barrier to dislocation due to two major reasons.

1. Crystallographic misorientation of the grains
2. Atomic disorder within a grain boundary resulting in discontinuity of slip planes.

Thus the grain boundaries are barriers to dislocation motion. Consequently as the grain size is decreased, the number of barriers increases and this is reflected in increased yield strength.

It may however be noted that fine grain size is not desirable for creep resistance as grain boundary sliding can cause creep elongation/cavitation.

Precipitation/dispersion Strengthening

Precipitates are obstacles to the motion of dislocation. There are two mechanisms for strengthening by this method – Multiphase Metals and Precipitation Strengthening.

Multiphase Metals

In this method, strengthening the metal is carried out by adding elements that have no or partial solubility in the parent metal. This will result in the appearance of a second phase distributed throughout the crystal or between crystals (e.g. Fe₃C, called as Cementite). This secondary phase can raise or reduce the strength of an alloy.

The properties of a polyphase (two or more phase) material depend on the nature, amount, size, shape, distribution, and orientation of the phases.

For example, in case of hypoeutectoid steels, carbon as cementite in pearlite increases strength of steel where as in case of steel beyond the eutectoid composition (hypereutectoid steels), the strength levels off or even reduces due to presence of proeutectoid cementite network. The hardness, however continues to increase due to the greater proportion of hard cementite

Precipitation Hardening

In designing alloys for strength, an approach often taken is to develop an alloy with a structure that consists of particles (which impede dislocation movement) dispersed in a ductile matrix. Such a dispersion can be obtained by choosing an alloy that is a single phase at elevated temperature but on cooling will precipitate another phase in the matrix. A thermal process is then developed to produce the desired distribution of precipitate in the matrix. When the alloy is strengthened by this thermal treatment, it is called precipitation strengthening or hardening.

Precipitation hardening consists of three main steps: solution treatment, quenching, and aging. Solution treatment involves heating the alloy to a temperature that allows the alloying atoms (called the solute) to dissolve into the solution. This results in a homogeneous solid solution of one phase. Quenching rapidly cools the solution and freezes the atoms in solution. In more technical terms, the quenching cools the material so fast that the atoms of the alloying elements do not have time to diffuse out of the solution. In the as-quenched condition, the solute is supersaturated meaning that the lattice is overly stressed by the alloying atoms. Aging is the process where the solute particles diffuse out of solution and into clusters that distort and strengthen the material.

Solute atoms in a solid solution and precipitates both are obstacles to the motion of dislocation. However precipitates are having pronounced effect on strengthening. The strengthening by the two methods can be compared by a real life example – difficulty with pebbles and boulders on a road.

Solute atoms are like pebbles
Precipitates are like boulders